Parametric Linear Bushing

thingiverse

This is a fully parametric linear bushing. You can change the length, inner and outer diameters, number of "spokes", height of spokes, width of spokes, etc. and Free CAD will automatically update the model accordingly. The more bushing surface area is in contact with the rod, the more friction you will have. A bushing with "spokes" allows you to decrease friction by reducing the total surface area in contact with the rod. You can modulate this via the BushingLength, SpokeWidth and SpokeCount parameters in the DIMS spreadsheet in the FreeCAD model. Shorter bushings have less contact, and so less friction. Thinner spokes have less contact and so less friction. Fewer spokes have less contact and so less friction, etc. However, reducing surface area also reduces the strength of the bushing to outside forces, so you'll have to experiment to find the right balance for your use.